U.S. patent application number 11/908187 was filed with the patent office on 2008-08-14 for belt tensioner with wear compensation.
Invention is credited to James W. Dell, Hubertus G. Mevissen.
Application Number | 20080194366 11/908187 |
Document ID | / |
Family ID | 37023344 |
Filed Date | 2008-08-14 |
United States Patent
Application |
20080194366 |
Kind Code |
A1 |
Mevissen; Hubertus G. ; et
al. |
August 14, 2008 |
Belt Tensioner with Wear Compensation
Abstract
A novel tensioner for use with flexible drives, such as
serpentine accessory belts on automobiles includes a tensioner arm
to spindle pivot design which employs a frustoconical bushing
between an inner pivot surface of the tensioner arm and a spindle
shaft. The frustoconical design of the bushing resists off axis
movement of the tensioner arm and a wear take up mechanism biases
the bushing into contact with the inner pivot surface to compensate
for normal wear of the bushing and/or pivot surface. A thrust plate
is mounted to the end of the spindle shaft and rides in a thrust
washer, the thrust plate and thrust washer being held captive in
the tensioner arm such that the tensioner arm can pivot about the
bushing and the spindle and the thrust plate and thrust washer
assist in inhibiting off-axis movement of the tensioner arm. In one
embodiment, the biasing force which biases the bushing against the
inner pivot surface of the tensioner arm can be varied to change
the amount of dampening of the tensioner.
Inventors: |
Mevissen; Hubertus G.;
(Schomberg, CA) ; Dell; James W.; (Newmarket,
CA) |
Correspondence
Address: |
MAGNA INTERNATIONAL, INC.
337 MAGNA DRIVE
AURORA
ON
L4G-7K1
omitted
|
Family ID: |
37023344 |
Appl. No.: |
11/908187 |
Filed: |
March 20, 2006 |
PCT Filed: |
March 20, 2006 |
PCT NO: |
PCT/CA2006/000422 |
371 Date: |
September 10, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60663853 |
Mar 21, 2005 |
|
|
|
Current U.S.
Class: |
474/135 |
Current CPC
Class: |
F16H 2007/081 20130101;
F16H 7/1281 20130101; F16H 7/1218 20130101 |
Class at
Publication: |
474/135 |
International
Class: |
F16H 7/12 20060101
F16H007/12 |
Claims
1. A tensioner to tension a flexible drive, comprising: a spindle
having a base and a shaft extending perpendicular thereto; a
bushing having an outer frustoconical surface and an inner surface
complementary to the shape of the spindle shaft, the bushing
receiving the shaft in its inner surface; a tensioner arm having a
pivot surface complementary to and engaging the outer frustoconical
surface of the bushing to allowing the tensioner arm to pivot about
a central axis of the spindle shaft, the tensioner arm further
having an attachment point for a rotatable member to engage a
flexible drive, the attachment point being spaced from the pivot
surface; a spring acting between the spindle and the tensioner arm
to bias the tensioner arm to a first pivotal position about the
spindle; and a wear take up mechanism to bias the bushing towards
the pivot surface to compensate for wear of the bushing and/or
pivot surface.
2. The tensioner of claim 1 further comprising a rotatable member
to engage a flexible drive, the rotatable member being mounted to
the attachment point of the tensioner arm via a bearing.
3. The tensioner of claim 2 wherein the rotatable member is a
pulley and the bearing is a roller bearing.
4. The tensioner of claim 1 wherein the wear take up mechanism
comprises a spring acting between the spindle and the bushing.
5. The tensioner of claim 4 further comprising a bushing guide
moveable within the spindle and including at least one tab
extending through a slot from within the spindle to the bushing
wherein the spring acts between the spindle and the bushing guide
and the bushing guide biases the bushing towards the pivot
surface.
6. The tensioner of claim 4 wherein the spring is a coil
spring.
7. The tensioner of claim 4 wherein the spring is an elastomeric
element.
8. The tensioner of claim 1 wherein the tensioner arm includes a
slot to receive a thrust plate and a thrust washer and wherein the
thrust plate is affixed to the end of the spindle about the central
axis of the shaft to keep the thrust plate and thrust washer
captive in the tensioner arm, the thrust plate being operable to
inhibit the tensioner arm from movement off-axis with respect to
the central axis of the shaft.
9. The tensioner of claim 1 wherein the wear take up mechanism
comprises a solenoid which is electrically operable to vary the
force with which the bushing is biased towards the pivot
surface.
10. The tensioner of claim 1 wherein the wear take up mechanism
comprises a hydraulic actuator which is operable to vary the force
with which the bushing is biased towards the pivot surface.
11. The tensioner of claim 1 wherein the radial diameter of the
shaft decreases in a series steps from the base of the spindle and
the inner surface of the bushing has a shape which is complementary
to the shape of the shaft.
12. The tensioner of claim 1 wherein the wear take up mechanism
mitigates changes in operation of the tensioner due to thermal
expansion.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a tensioner which operates
to maintain a substantially constant tension in a flexible drive,
such as a belt or chain. More specifically, the present invention
relates to a tensioner which includes means to compensate for the
wear of components of the tensioner which occurs during use.
BACKGROUND OF THE INVENTION
[0002] Tensioners for flexible drives, such as accessory serpentine
belts on automotive engines are well known. Such tensioners
typically include a pulley, roller or other member, which is biased
against the flexible drive by a spring or other biasing means. The
pulley is mounted, via a bearing, to an arm which pivots with
respect to the tensioner housing. The housing contains the spring
or other biasing means which biases the arm towards the flexible
drive to maintain a substantially constant tension in the flexible
drive. Conventional tensioners can also include frictional members
which ride on one another as the tensioner arm moves to provide a
dampening force to the tensioner.
[0003] While such prior art tensioners are widely employed, they do
suffer from some disadvantages. In particular, due to the
relatively large forces which must be carried by the tensioner arm,
wear at the pivot attaching the arm to the tensioner housing is
common and such wear can result in the pulley moving to an off-axis
position wherein the surface of the pulley is not substantially
perpendicular to the engagement surface of the flexible drive. Such
off-axis positioning of the pulley results in increased amounts of
wear at the pivot and eventually will result in the flexible drive
being damaged and/or slipping off the tensioner pulley
altogether.
[0004] It is desired to have a tensioner which provides a suitable
dampening force, can provide compensation for normal wear of its
components and which resists off-perpendicular movement of its
components.
SUMMARY OF THE INVENTION
[0005] It is an object of the present invention to provide a novel
tensioner which obviates or mitigates at least one disadvantage of
the prior art.
[0006] According to a first aspect of the present invention, there
is provided a tensioner to tension a flexible drive, comprising: a
spindle having a base and a shaft extending perpendicular thereto;
a bushing having an outer frustoconical surface and an inner
surface complementary to the shape of the spindle shaft, the
bushing receiving the shaft in its inner surface; a tensioner arm
having a pivot surface complementary to and engaging the outer
frustoconical surface of the bushing to allowing the tensioner arm
to pivot about a central axis of the spindle shaft, the tensioner
arm further having an attachment point for a rotatable member to
engage a flexible drive, the attachment point being spaced from the
pivot surface; a spring acting between the spindle and the
tensioner arm to bias the tensioner arm to a first pivotal position
about the spindle; and a wear take up mechanism to bias the bushing
towards the pivot surface to compensate for wear of the bushing
and/or pivot surface.
[0007] The present invention provides a novel tensioner for use
with flexible drives, such as serpentine accessory belts on
automobiles or the like. The tensioner includes a tensioner arm to
spindle pivot design which employs a frustoconical bushing between
an inner pivot surface of the tensioner arm and a spindle shaft.
The frustoconical design of the bushing resists off axis movement
of the tensioner arm and a wear take up mechanism biases the
bushing into contact with the inner pivot surface to compensate for
normal wear of the bushing and/or pivot surface. A thrust plate is
mounted to the end of the spindle shaft and rides in a thrust
washer, the thrust plate and thrust washer being held captive in
the tensioner arm such that the tensioner arm can pivot about the
bushing and the spindle and the thrust plate and thrust washer
assist in inhibiting off-axis movement of the tensioner arm.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Preferred embodiments of the present invention will now be
described, by way of example only, with reference to the attached
Figures, wherein:
[0009] FIG. 1 shows a perspective exploded view of a tensioner in
accordance with the present invention;
[0010] FIG. 2 shows a spindle for the tensioner of FIG. 1;
[0011] FIGS. 3a and 3b shows a perspective top and bottom view,
respectively, of a tensioner arm for the tensioner of FIG. 1;
[0012] FIG. 4 shows a perspective view of a bushing for the
tensioner of FIG. 1;
[0013] FIG. 5 shows a side cross section view of the assembled
tensioner of FIG. 1;
[0014] FIG. 6 shows a wear take up mechanism for the tensioner of
FIG. 1;
[0015] FIG. 7 shows a thrust plate and thrust washer for the
tensioner of FIG. 1; and
[0016] FIG. 8 shows another embodiment of a spindle for the
tensioner of FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0017] A tensioner in accordance with the present invention is
indicated generally at 20 in FIG. 1. Tensioner 20 comprises a
spindle 24, best seen in FIG. 2, which includes a base 28 to abut
an engine (not shown) when tensioner 20 is installed. Base 28 can
include one or more index features, such as tab 32, which can
engage complementary features on an engine to ensure that tensioner
20 is installed in, and remains in, a desired rotational
orientation on the engine. Spindle 20 further includes a
cylindrical shaft 36, which extends from base 28, and a spring
raceway 40 with an endstop 44.
[0018] A helical spring 48 acts between spindle 24 and a tensioner
arm 50, best seen in FIGS. 3a and 3b. In the illustrated
embodiment, spring 48 is expanded as tensioner arm 50 is moved from
its at rest position. In this configuration, spring 48 includes a
first end which abuts endstop 44 when helical spring 48 is received
in raceway 40 in spindle 24 and the opposite end of helical spring
48 abuts an endstop 52 on tensioner arm 50 when spring 48 is
received in a raceway 56 in tensioner arm 50.
[0019] While it is presently preferred that spring 48 expand as
tensioner arm 50 is moved from its at rest position as this avoids
the expense for forming tangs at the ends of spring 48, it is also
contemplated that spring 48 can be arranged to be contracted as
tensioner arm 50 is moved from its at rest position. In this
configuration spring 48 will typically be provided with a bent tang
at each end and tensioner arm 50 and spindle 24 will be provided
with grooves or apertures to capture and retain the respective
spring tangs.
[0020] Tensioner arm 50 is pivotally mounted to shaft 36 of spindle
24 and is biased towards the flexible drive (not shown) to be
tensioned by helical spring 48. Specifically, a bearing 60, best
seen in FIG. 4, includes a cylindrical inner aperture 64 into which
shaft 36 of spindle 24 is inserted. Inner cylindrical aperture 64
further includes at least one feature to index bearing 60 on shaft
36 to prevent rotation of bearing 60 on shaft 36. In the
illustrated embodiment, bearing 60 includes three ribs 72, 76 and
80 which engage complementary slots 84, 88 and 92 respectively to
prevent bearing 60 from rotating on shaft 36 while allowing bearing
60 to be moved along shaft 36. The outer surface 68 of bearing 60
is frustoconical in shape, with bearing 60 receiving shaft 36 such
that the large radius end of surface 68 is adjacent base 28.
[0021] Tensioner arm 50 includes an inner pivot surface 96 which is
complementary in shape to outer surface 68 of bearing 60. When
assembled, as shown in FIG. 5, pivot surface 96 rides on outer
surface 68 to allow tensioner arm 50 to pivot about the centerline
of shaft 36.
[0022] Returning to FIG. 4, bearing 60 is preferably made from a
material such as Delrin.TM., or other reasonably hard nylon, which
allows inner surface 96 of tensioner arm 50 to pivot on outer
surface 68 as tensioner 20 operates, without undue wear of either
inner surface 96 or outer surface 68 occurring. As is also shown in
FIG. 4, bearing 60 is preferably fabricated with a break 100, which
provides some accommodation for manufacturing tolerances of shaft
36 and/or bearing 68, and at least one debris groove 104 on outer
surface 68 and at least one debris groove 108 on inner surface 64.
Debris grooves 104 capture water and/or foreign materials entrapped
between outer surface 68 and inner surface 96 and allow the debris
to travel along grooves 104 and exit tensioner 20 to reduce wear of
the respective surfaces from entrapped debris. Similarly, debris
grooves 108 capture water and/or foreign materials entrapped
between inner surface 64 and the outer surface of shaft 36 and
allow the debris to travel along grooves 108 and exit tensioner 20
to reduce wear of the respective surfaces from entrapped
debris.
[0023] As will be apparent to those of skill in the art, despite
the appropriate selection of a material to fabricate bushing 60 and
the provision of debris grooves 104 and 108, outer surface 68 of
bushing 60 will eventually wear under normal use. Accordingly, in
the present invention, as wear of outer surface 68 occurs, bushing
60 is urged away from base 28 along shaft 36 by a wear take up
mechanism and this results in outer surface 68 being maintained in
full contact with inner pivot surface 96 despite wear of outer
surface 68.
[0024] In the embodiment of the present invention illustrated in
FIGS. 1 through 7, the wear take up mechanism comprises a bushing
guide 112 and a compression spring 116, best seen in FIG. 6.
Bushing guide 112 includes tabs 120 which extend through slots 124
in shaft 36 to engage tab receiving grooves 128 in the base of
bushing 60. Compression spring 116 is pressed into spindle 24 with
bushing guide 112 and compression spring 116 acts between the inner
surface of base 28 and bushing guide 112 to bias bushing guide 112
away from base 28. As tabs 120 engage bushing 60, the biasing force
of spring 116 is applied to bushing 60 and outer surface 68 is
biased into contact with inner pivot surface 96.
[0025] Spring 116 can be of a wide variety of types and/or designs,
as will occur to those of skill in the art, to achieve a desired
dampening function for tensioner 20. For example, spring 116 can be
a straight coil (i.e.--linear) spring, a tapered coil spring, an
elastomeric spring such as a synthetic rubber member, a closed cell
foam spring, etc. Selection of an appropriate spring design is
within the normal skills of those of skill in the art and will not
be further discussed herein.
[0026] It is also contemplated that, in some embodiments, bushing
guide 112 can be omitted and spring 116 can act directly against
bushing 60 via a tang or other feature that extends through slots
124 to engage the end of bushing 60.
[0027] As will now be apparent to those of skill in the art, by
biasing bushing 60 toward tensioner arm 50, outer surface 68 of
bushing 60 is maintained in contact with inner pivot surface 96,
despite wear of bushing 60 which may occur in normal use of
tensioner 50. By maintaining outer surface 68 in contact with inner
pivot surface 96, off-axis movement (i.e.--tilt) of tensioner arm
50 is prevented. Further, as is understood by those of skill in the
art, the friction between outer surface 68 of bushing 60 and inner
pivot surface 96 acts as a dampening force to reduce oscillations
of tensioner arm 50 during operation. By biasing bushing 60 toward
tensioner arm 50 to maintain contact of outer surface 68 with inner
pivot surface 96, the dampening force created therebetween is
substantially constant, despite normal wear of bushing 60. Further,
changes in the dampening force between tensioner arm 50 and spindle
24 and/or changes to the alignment of tensioner arm 50 and spindle
24 which may otherwise occur due to thermal expansion of components
of tensioner 20 are mitigated by the above described movement of
bushing 60 along shaft 36, towards and/or away from inner pivot
surface 96.
[0028] As shown in FIGS. 1 and 5, a rotatable member is connected
to tensioner arm 50 to engage the flexible drive and apply the
tensioning force created by tensioner 20 to the flexible drive. In
the illustrated embodiment, the rotatable member comprises a pulley
132 with a roller bearing 136 which allows it to rotate freely with
a flexible drive about a bolt 140 by which it is mounted to
tensioner arm 50. While in the illustrated embodiment, bearing 136
is a separate component, it is also contemplated that in other
embodiments bearing 136 can be integrally formed with pulley 132 if
desired. Bolt 140 engages an internally threaded bore 144 in
tensioner arm 50.
[0029] Tensioner arm 50 is mounted to spindle 24 by a thrust plate
148 and thrust washer 152, best seen in FIG. 7. Thrust washer 152
includes indexing tabs 156 to prevent rotation of thrust washer
152, with respect to tensioner arm 50, when tensioner 20 is
assembled. To assemble tensioner 20, thrust washer 152 is inserted
into a slot 160 (best seen in FIG. 3a) in tensioner arm 50. Slot
160 includes index grooves 164 which are complementary to index
tabs 156 on thrust washer 152 and which engage index tabs 156 when
thrust washer 152 is inserted into slot 160.
[0030] Once thrust washer 152 is in place in slot 160, thrust plate
148 is inserted into a slot 168 in thrust washer 152. As shown in
FIG. 2, spindle 24 includes a set of staking posts 172 and thrust
plate 148 includes a complementary set of staking bores 176. When
thrust washer 152 and thrust plate 148 are assembled in tensioner
arm 50, the resulting assembly can be joined to spindle 24 and
helical spring 48 with staking posts 172 being received in staking
bores 176 and tensioner 20 permanently joined, as shown in FIG. 5,
by compressing and flaring staking posts 172 in bores 176. A center
bore 178 in thrust plate 148 aligns with a similar center bore 180
in spindle 24 and these bores allow tensioner 20 to be installed on
an engine or other device by a bolt or other fastener passing
therethrough.
[0031] In the illustrated embodiment, thrust plate 148 includes a
limit tang 182 which extends radially outwardly and then downwardly
from thrust plate 148 and tensioner arm 50 includes a pair of end
stops 184 and 188 which limit tang 180 will abut at each end of the
intended operating range of tensioner 20 to limit further rotation
of tensioner arm 50. As will be apparent to those of skill in the
art, a wide variety of other geometries can be employed for limit
tang 180 and/or end stops 184 and 188 to provide a desired
operating range for tensioner 20. Thrust washer 162 is preferably
fabricated from a material similar to that from which bushing 60 is
fabricated to allow rotation of tensioner arm 50 with respect to
spindle 24 and thrust plate 148.
[0032] It is believed that the design and arrangement of thrust
washer 152, thrust plate 148 and tensioner arm 50 provide
advantages to tensioner 20. In particular, the large radial
diameter of thrust plate 148 against which tensioner arm 50 rides,
via thrust washer 152, provides a large surface and moment arm to
prevent off-axis movement of tensioner arm 50 and pulley 132.
Further, the frictional force developed between thrust plate 148
and thrust washer 152 provide further dampening for tensioner
20.
[0033] As mentioned above, off-axis movement of tensioner arm 50
and/or pulley 132 can result in increased wear of tensioner 20
and/or the flexible drive means being tensioned and, if the
off-axis movement is sufficient to allow the flexible drive means
to move off of pulley 132, failure of the flexible drive means.
Accordingly, the novel wear compensation mechanism of the present
invention is believed to afford significant advantages in reducing
off-axis movement of tensioner arm 50. Further, the novel
arrangement of thrust plate 148 and thrust washer 152 with
tensioner arm 50 advantageously further reduces off-axis movement
of tensioner arm 50 and pulley 132.
[0034] While it is important for proper operation of flexible drive
means, such as accessory serpentine belt drive on automobiles, that
their tensioners provide adequate dampening to the flexible drive,
it is contemplated by the present inventors that it can be
advantageous to have the ability to vary the amount of dampening
for different operating conditions. Accordingly, it is contemplated
that compression spring 116 of the wear take up mechanism of the
present invention can be replaced by, or used in conjunction with,
a controllable actuator, such as an electric solenoid or a pressure
actuator, such as a pneumatic actuator supplied with pressurized
engine lubricating oil. In such a case, the amount of dampening
produced by the frictional force between bushing 60 and tensioner
arm 50 can be varied by altering the biasing force applied to
bushing 60 by the wear take up mechanism. When high mounts of
dampening are required, increased biasing force can be applied to
bushing 60 to increase the frictional force developed between outer
surface 68 and inner pivot surface 96. When lower amounts of
dampening are required, a reduced biasing force can be applied to
bushing 60 to decease the frictional force developed between outer
surface 68 and inner pivot surface 96. However, in either
circumstance, it is contemplated that sufficient biasing force will
always be applied to bushing 60 to compensate for wear.
[0035] A second embodiment of a spindle 200 for tensioner 20 is
illustrated in FIG. 8 wherein like features to those of spindle 24
are indicated with like reference numbers with an "a" appended
thereto. In this embodiment, shaft 36a of spindle 200 is formed
with a series of small step-like decreases in the radius of shaft
36a. As will be apparent to those of skill in the art, by forming
spindle 200 with shaft 36a having such small decreases in its
radius, the expense of manufacturing and operating molds for
spindle 200 is reduced from that of spindle 24. If spindle 200 is
to be used in tensioner 20, the inner surface 64 of bushing 60 will
be formed in a slightly frustoconical shape complementary to the
shape of shaft 36a and, in conjunction with break 100 in bushing
60, bushing 60 will still ride on shaft 36a with sufficient
alignment to provide the desired resistance to off-axis movement of
tensioner arm 50.
[0036] The present invention provides a novel tensioner for use
with flexible drives, such as serpentine accessory belts on
automobiles. The tensioner includes a tensioner arm to spindle
pivot design which employs a frustoconical bushing between an inner
pivot surface of the tensioner arm and a spindle shaft. The
frustoconical design of the bushing resists off axis movement of
the tensioner arm and a wear take up mechanism biases the bushing
into contact with the inner pivot surface to compensate for normal
wear of the bushing and/or pivot surface. A thrust plate is mounted
to the end of the spindle shaft and rides in a thrust washer, the
thrust plate and thrust washer being held captive in the tensioner
arm such that the tensioner arm can pivot about the bushing and the
spindle and the thrust plate and thrust washer assist in inhibiting
off-axis movement of the tensioner arm.
[0037] In one embodiment, the biasing force which biases the
bushing against the inner pivot surface of the tensioner arm can be
varied to change the amount of dampening of the tensioner.
[0038] The above-described embodiments of the invention are
intended to be examples of the present invention and alterations
and modifications may be effected thereto, by those of skill in the
art, without departing from the scope of the invention which is
defined solely by the claims appended hereto.
* * * * *